The invention relates to a soil-compacting device comprising a soil contact element actuated by a vibration generator for the purpose of soil compaction.
Such a soil-compacting device, for example a vibrating plate or vibrating roller, is usually composed of two masses coupled elastically relative to one another, specifically a lower mass and an upper mass. The lower mass substantially comprises a soil contact element which is actuated by a vibration generator. The upper mass usually carries a drive for the vibration generator and is connected to the lower mass via spring elements. Vibration generators which have proved to be useful in the past have been unbalanced generators in which one or two shafts bearing unbalanced masses are set in rotation. The vibration produced thereby, which, if required, can also be set in different directions, is introduced into the soil contact element and used for the compaction of soils. The structure described is generally known, in particular in connection with vibrating plates or vibrating rollers, so that a further description is not necessary.
In the case of such soil-compacting devices, the vibration generators usually produce a vibration with constant frequency and amplitude. In addition, there are known vibrating plates in which, although a stepped or stepless adjustment of frequency and/or amplitude is possible, the adjustment is the sole responsibility of the operator. Since the optimum parameters for soil compaction can constantly change during the compaction operation on account of different soil characteristics, and since the operator is not able to constantly detect these parameters and translate them into a corresponding adjustment of the vibration generator, the vibration parameters are generally not matched to the particular properties of the ground. In this respect, the problem may occur in particular that the soil-compacting device starts to jump if the soil to be compacted does not have sufficient deformability. Jumping of the soil-compacting device leads to a rapid increase in machine wear and in environmental noise pollution and puts a strain on the operator. In addition, jumping of the soil-compacting device can cause the soil to loosen up again. WO98/17865 discloses a method of measuring mechanical data of a soil for a soil-compacting device. Described therein is a vibrating roller whose roller tire, together with the soil to be compacted, is regarded as a compaction vibration system whose vibration behavior is detected by a computer unit. The computer unit adjusts the vibration generator in the vibrating roller in such a way that a predetermined soil rigidity, that is to say the desired outcome of compaction, can be achieved. The vibration behavior is recorded by means of a plurality of measuring elements which are mounted on the roller tire serving as the soil contact element.
It has been found to be the case in various soil-compacting devices that, because of numerous external influences such as the actuation by the vibration generator, and also as a result of constantly changing soil conditions, stones, unevennesses, etc., a random, occasionally wobbling movement of the soil contact element is brought about and can only be detected using highly complex measuring equipment.
It is an object of the invention to specify a soil-compacting device with a controllable vibration generator, in which device the vibration behavior of the soil contact element can be detected in a more simple manner.
Provision is made in the soil-compacting device according to the invention for a detection mass which is connected to the soil contact element by means of an elastic coupling. The detection mass can be moved with at least one degree of freedom relative to the elastic coupling with the soil contact element, the movement of the detection mass being measured by a measuring means. A measuring signal emitted by the measuring means is evaluated in a control means and compared with a setpoint value. When a deviation is established, the control means correspondingly activates the vibration generator actuating the soil contact element.
The detection mass and the soil contact element form a mechanical filter which is used to filter substantially stochastic movements, i.e. vibrations, which prevail at the soil contact element in such a manner that it is possible, for example, for higher-frequency vibrations, that is to say vibrations with a frequency higher than the frequency predetermined by the vibration generator, to be filtered out, so that the detection mass is subject to a movement and vibration pattern which is simplified in relation to the soil contact element. To be specific, the filtering can be carried out in such a way that, although the vibrations generated as a result of the reaction to an excessive impact energy, that is to say, for example, vibrations generated by the jumping of the soil contact element, occur at the detection mass, the stochastic vibrations of the lower mass comprising the soil contact element do not.
This vibration of the detection mass can be detected in a considerably simpler manner compared with the prior art with the aid of the measuring means, so that an unambiguous measuring signal is available for the control means.
In order to refine the measuring method, the measuring means is suitable, in an advantageous development of the invention, for detecting movements of the detection mass in a plurality of spatial directions and/or directions of rotation.
In a particularly advantageous embodiment of the invention, the detection mass is formed by the upper mass. The upper mass is elastically coupled to the lower mass, so that no additional detection mass element need be provided. For this purpose, the measuring means detects the movement of the upper mass and delivers a corresponding measuring signal. By virtue of the relatively high inertia of the upper mass, the filter action is used with particular advantage. The structure can be realized in a simple manner since only one measuring means need be mounted on the upper mass.
The movement measured by the measuring means is preferably an acceleration of the detection mass, since acceleration values can be measured particularly simply.